This invention relates to an asynchronous transfer mode (ATM) exchange or switching system and, more particularly, to the individual modules used in the ATM exchange system. The ATM exchange system is also referred to as an asynchronous time division exchange system.
In connection with an asynchronous time division exchange system, one of the modules will be taken into consideration and will herein be called a local module. In the manner which will later be described more in detail, the local module is connected through a highway bus to other modules of the asynchronous time division exchange system. In the manner known in the art, the asynchronous time division exchange system switches transmission data among the local and the other modules in accordance with an ATM mode.
Each of the local and the other modules comprises a connection control unit connected to the highway bus and a plurality of connection ports connected to the connection control unit through a module bus. Each of the connection ports is for dealing with a transmission signal. The transmission data comprise such transmission signals and control data for use in controlling switching of the transmission data.
In a conventional asynchronous time division exchange system, the transmission data are usually transmitted as data packets. More particularly, each connection port processes each transmission signal into a data packet including, besides a logic channel group number (LCGN), a logic channel number (LCN) which serves as a virtual channel identifier (VCI) standardized by the CCITT and by a broad-band ISDN recommendation series. The logic channel number therefore indicates, as a destination module, one of the local and the other modules that should receive the transmission signal.
For convenience of the description which follows, each of the local and the other modules will be called a particular module. The connection control unit of the particular module checks the logic channel number which is included in the data packet received through the highway bus. When the particular module is the destination module, the connection control unit transfers the data packet to the module bus of the destination module. Otherwise, the data packet is a spurious or unnecessary packet insofar as the particular module is concerned. Such spurious packets are transmitted through the highway bus.
Inasmuch as the connection control unit must check not only the data packet directed to the particular module but also the unnecessary packets, operation of the conventional asynchronous time division exchange system is troublesome. It takes a long time for the connection control unit to discriminate between the data packet directed to the particular module and the spurious packets. This results in a defect of adversely affecting performance of the exchange system.
A great number, such as scores of thousands, of the logic channel numbers are often used. In such an event, the above-mentioned defect gives rise to a serious disadvantage in that a large-scaled connection control unit becomes indispensable.